The present invention relates generally to optoelectronic devices, and, more particularly, to a multiple quantum well optoelectronic devices for emission and modulation of light.
Optical networks require increasingly sophisticated function in the optical domain. Additionally, self-sustained microwave-frequency oscillation is also required to serve as a subcarrier for signals generated and distributed over optical fibers. The present invention addresses limitations in the rate at which higher bandwidth modulation of an optical signal may be achieved by accomplishing the coupling of electronic and optical functions within a single device, thereby circumventing the limiting parasitic effects of external circuitry.
Various mechanisms are believed to impede interwell transport of carriers among the layers of a stack of multiple quantum wells, with carriers of each conductivity type distinctly affected. The result of the mechanisms is a nonuniformity in the distribution of carriers among the various quantum wells of a stack. Carrier density nonuniformity has been seen as limiting device performance.
Other quantum-well-based optical devices, such as described in U.S. Pat. No. 5,673,140, rely on the modulation of refraction or of absorption and thus require an external light source. Further examples of quantum-well based optoelectronic devices are provided by Meyer et al., Electronics Letters, vol. 32, pp. 45-46, (1996), Shen et al., IEEE Electron Device Letters, vol. 16, pp. 178-180 (1995), and Yang et al., Applied Physics Letters., vol. 59, pp. 181-182, (1991), all of which references are incorporated herein by reference. The modulation of an active light-emitting device, however, requires the modulation of a positive gain which has not been known to be possible, and is addressed for the first time in the teachings of the present invention.
Devices known to exhibit tunneling phenomena are currently limited either to those exhibiting tunneling from one band to another, in the manner of Esaki diodes, or else are restricted to unipolar devices to which carriers of only a single type exhibit intraband tunneling behavior. Such devices are exemplified by those described in Brown et al., xe2x80x9cOscillations up to 420 GHz in GaAs/AlAs resonant tunneling diodes,xe2x80x9d Applied Physics Letters vol. 55, p. 777 (1989).
In accordance with preferred embodiments of the present invention, there is provided an optical semiconductor device. The semiconductor device has a stack of a plurality of layers of semiconducting material. Within the plurality of layers, at least one quantum well is bounded on each of two sides by an energy barrier with respect to transport of a charge carrier between the at least one quantum well and adjoining material on each of two sides, and the quantum well having at least two bound quantum states with respect to a trapped charge carrier. The device also has an optically active zone including the at least one quantum well, with the optically active zone characterized by an optical gain under forward operation of the device. The device has a first carrier injector for forward-injecting carriers of a first conductivity type into the at least one quantum well and a second carrier injector for forward-injecting carriers of a second conductivity type into the optically active zone at in such a way as to vary the optical gain of the optically active zone.
In accordance with alternate embodiments of the invention, the quantum well may be bounded by two barriers with respect to the transport of holes or with respect to the transport of electrons, or both. One of the barriers may be approximately triangular, so as to enable field-emission through the at least one barrier. In accordance with further embodiments of the invention, thermionic transport of at least one carrier type into the at least one quantum well is precluded at a specified operating temperature and transport of at least one carrier type into the at least one quantum well is by means of resonant tunneling or field-emission tunneling.
In accordance with yet further embodiments of the invention, a non-linear optical semiconductor device is provided that has a a stack of a plurality of layers of semiconducting material having at least one quantum well bounded on each of two sides by an energy barrier with respect to transport of a charge carrier between the at least one quantum well and adjoining material on each of two sides. Electrical current through the stack is a nonmonotonic function of an applied electrical potential across the stack. The device has an associated circuit for modulating an optical gain of a region of the stack by virtue of the nonlinear function of current versus applied electrical potential.